Aircraft heating apparatus



Sept. 9, 1947. H. J. DE N. M COLLUM 2,427,221

' AIRCRAFT HEATING APPARATUS Filed Jan. 15, 1943 Z5 She'ets-Sheet l W 1767K 7/26 wza aacmaz J 4% Wicf/zaaa, isecu rz'z Mam @7 MI- Sept. 9, 1947. H. J. DE N. M COLLUM AIRCRAFT HEATING APPARATUS Filed Jan. 15, 1945 3 Sheets-Sheet 2 Sept. 9, 1947. 1 J, DE N. McCOLLUM 2,427,221

I AIRCRAFT HEATING APPARATUS Filed Jan. 15, 1945 s Sheets-Sheet s I I a ms 0221115.

Patented Sept. 9, 1947 UNITED STATES PATENT OFFICE AIRCRAFT HEATiNG APPARATUS Henry J. De N. McCollum, Chicago, Ill.; Thelma McColIum, executrix of said Henry J. De N.

McCollum,

Warner Corporation tion of Virginia deceased, assignor to Stewart- Chicago, 111., a corporae Application January 15, 1943,Serial No. 472,458"

weight of the apparatus are severe, and as a result it is necessary that the apparatus be, as far as possible, devoid of heavy components and that, if necessary, high efiiciency of operation may be partially sacrificed in favor of lightness inweight,

although the considerations of the weight of the apparatus must be balanced against the weight of the fuel required for a given heat output. Another factor which imposes a substantial limitation upon the construction and design of aircraft heating apparatus is due to the extremes of temperature encountered, and the great variation in rate of heat losses fromthe airplane dependent upon the speed of flight. Another allimportant factor is the necessity of safety in operation, not only to eliminate fire hazard, but also to eliminate the possibility of the escape of the products of combustion from the heating apparatus to the air being heated. This is of course of paramount importance in the heating of the cabins of airplanes, since the products of combustion usually contain a toxic percentage of carbon monoxide.

A further consideration for which allowance must be made in the design of the apparatus is that, considering'the Volume of the space to be heated, heated air must be supplied at a high volumetric rate in order to compensate for prob- 1 able substantial leakage of air through cracks and openings in the skin of the cabin, and to assure a sufilcient addition of heat to the space within the cabin, since the heat losses, by conduction and radiation, as well as due to the escape of heated air from the cabin, are extremely high.

Furthermore, the extreme changes in atmospheric pressure, and the extremely low atmospheric temperature at which combustion must be maintained, are factors which present additional difiiculties which must be overcome in the construction and design of aircraft heaters. The possibility of encountering icing conditions is a further factor to be considered.

In the invention disclosed herein,,allowance is made for the limitations in construction and de- Claims. 01. 237432) sign imposed by the foregoing and other factors.

;liable in operation, and which may For example, the requirement of minimum weight is met in part by utilizing air rams or scoops as a source of air under pressure for supplying not only the air necessary for combustion, but also the ventilating air.

It is thus a primary object of my invention to provide an improved aircraft heating apparatus which is light in weight, which is capable of efficient operation under the widely varying atmospheric temperature and pressure conditions which are encountered, in which the possibility of the escape of toxic products of combustion to the ventilating air is eliminated, which will be rebe economically manufactured. More specifically, it is among the objects of my invention to provide an improved aircraft heating apparatus, in which:

(l) Ventilating and combustion air is supplied to the heating apparatus from a common ram or scoop;

(2) The formationof ice around the ram, or scoop is avoided by supplying thereto heat derived from the heating apparatus; (3) The pressure within the combustion chamber, within the heat exchanger and in the exhaust conduit for the products of combustion is maintained at a lower value than that ofthe space surrounding these parts, so that even if a leak in these parts should develop, none of the products of combustion will escape tothe surrounding air, butuinstead the flow will be in the reverse direction; a

(4) The pressure drop through the fuel mixturesupplying conduits is sufiicient to cause the pressure within the combustion chamber, and

partsjconnected therewith, to be lower than that of the surrounding ventilating air;

(5) The flow of ventilating air from the heating apparatus is restricted in one or more of several ways, such as by a pressure responsive valve, or because of the frictional resistance of the duct system, so asv to maintain the pressure of the ventilating air surrounding the combustion chamber and heat exchanger at a value higher than, that within these parts;

(6) The pressure within the combustion chamber and heat exchanger is reduced by the use of a discharge conduit opening at a point alongthe external skin of the airplane at which flow of air from a ram or scoop to the heating apparatus in response to the dynamic air pressure;

(8) Air for both combustion and ventilation is supplied to the heating apparatus from a single ram or scoop, with provisions made to prevent reverse flow from the combustion chamber to the ventilating air space;

(9) The products of combustion leaving the heat exchanger of the apparatus are utilized to heat the air ram or scoop;

(10) The heat exchanger has primary heat exchange surfaces whereby the rate of heat transfer will increase with the velocity of flow upon the opposite sides thereof;

(11) The amount of heat generated and transferred to the ventilating air increases as the speed of the airplane increases, while under these circumstances the temperature of the ventilating air leaving the heating apparatus decreases slightly.

Other objects will appear from the following description,reference'being had to the accompanying drawings, in which: I Fig. 1 is a diagrammatic view of one form ofheating apparatus utilizing a pressure responsive valve for controlling the ventilating air pressure in the heat exchanger;

Fig. 2 is a longitudinal horizontal sectional view'of a heater utilizable in the installations of this invention;

Figs. 3 and 4' are transverse sectional views taken on the lines 3-3 and 44, respectively, of Fig. 2f;

Fig. 5 is a diagrammatic view of a heater installation illustrating an anti-icing air scoop;

Fig. 6' is a fragmentary sectional View taken on a line 6-6 of Fig. 5 and Fig. '7 is a diagrammatic view of a modified form of heater installation. 7

This application is a continuation in part of my copending application, Serial No. 373,751, filed January 9, 1941, in which was disclosed the apparatus substantially as shown in Fig. 1 of this application.

Fig. 1 discloses a heating system of a simple form which incorporates some, but not all, of the advantageous features of the. invention, the apparatus being shown as applied to an airplane having a supercharged cabin. In this figure the heater is illustrated as installed in the nacelle ID of an airplane, a portion of the apparatus, including the, fuel supply and carburetor, being located in front of a fire wall [2 to separate it from the heating unit enclosure 20. The direction, of 110W of the, air through the. heater is indicated by. arrows.

The portion of the apparatus in front of the fire wall l2 includes a blower 1.6. of sufiicient capacity to supercharge. the. cabin and maintain it at a pressure in excess of six inches of mercury above atmospheric pressure for conditions of high, altitude flight. Air issupplied to the blower through an air inlet conduit [4, which. preferablyv opens in the direction of. flight andmaybe in the form of a ram or scoop. Airis. discharged from the supercharger blower through. a conduit I-8- which passes through the fire wall l2 and connects the blower to the inlet of a heating unit assembly enclosure or casing 20. Within the enclosure 20- is a heating unit assembly comprising a number of heating units 22-, which may be of the general type disclosed in the prior patent of. Henry J. DeN. McCollum and Thomas F.

4 Spackman, No. 2,236,789, granted April 1, 1941.

A combustible mixture of fuel and air is supplied to these units from a supply duct 24 through a pair of intake manifolds 26, each manifold supplying a bank of five of the units 2 2 in the construction illustrated. A pair of exhaust manifolds 28 conduct the products of combustion from the heater units 22 to an exhaust conduit 30, which later discharges adjacent the outer surface of the airplane, preferably at a point at which the pressure is maintained below atmospheric pressure by the motion of the plane. Because of the pressure drop in the intake conduit 34 and a carburetor 32, the pressure in the combustion chamber is maintained below that of the ventilating air surrounding it.

The combustible mixture is supplied to the intake conduit 24 from the balanced carburetor 32. A fuel pump 36 causes fuel to flow from a suitable fuel supply source 31 through a fuel line 38 to the float bowl of the carburetor 32. A conduit 34 supplies air under pressure from the conduit 18 to the carburetor inlet. The inlet end of the conduit 34 is so disposed with respect to the direction of the flow of air in the conduit l8 that the air pressure in the conduit 34 will ordinarily be slightly less than that within the casing 20.

It is thus seen that under all conditions of operation, the combustion chambers and internal passageways of the heating units 22 are maintained at a lower pressure than the air passing over them. As. a result, should a leak develop in the walls of one of these units 22, air would flow into the unit, and none of the toxic gases of combustion could escape into the air being heated.

Heated air flOWs from the casing 20 through a conduit 40 into the cabin of the. airplane. Within the conduit 48: is a thermostatic control: element 42; which is connected by a rod 43 with a butterfly valve 44; to regulate the rate of flow of air through the carburetor air supply conduit 34. The thermostatic element 42 and valve 44: are constructed and arranged to increase the rate of flow of air to the carburetor as the temperature of the air within the conduit 40 drops, and to decrease this rate of flow as said temperature rises. thereby maintaining the temperature of the air passing into the cabin substantially constant at the. desired value.

The air in the casing 20. and conduit {.8 is maintained at a predetermined positive. pressure with respect to the. surrounding air (generally the at mosphericpressure). by a damper 46. which regulates the rate of flow of air through the outlet conduit 40, The pressure differential is pref,- erably slightly above the minimum necessary to maintainsteady. operation of the heater, and is ordinarily not great, I have found that a, pres.- sure differential in the order of two inches, of mercury is usually adequate. The damper 4.6, is

actuated by a rod 48 connected. to, a,v differential.

branched to convey the hot air to outlets suitably located for the heating of various compartments of the plane.

Under many circumstances, it is desirable that the heating apparatus be capable of operation while the airplane is on the ground. This may be desirable not only for the comfort of the crew in preparing for a flight, but in the event that the heating apparatus is used to melt ice which has formed upon the wings and control surfaces, it may be essential. The system shown in Fig. 1 may be operated while the airplane is on the ground because of the use of the blower It to supply the ventilating and combustion air.

In order to insure that the operation of the heater need not be interrupted due to building up an excessive temperature, and to avoid the necessity of providing additional thermostatic con trols, and further, to insure that the rate of heat output of the heater will increase substantially continuously as th'e speed of flight of the airplane increases, it is desirable that the heat exchanger consist solely or at least in great part, of primary heat transfer surfaces.

A heat exchanger having primary heat transfer surfaces is one in which the heat transfer from the hotter to the cooler fluid takes place through a wall separating the two fluids and of such thinness that the rate' of heat transfer is not materially influenced by the thermal conductivity of the wall, but is mainly dependent upon the rate at which the two fluids flow past the wall. A primary heat transfer surface is thus distinguished from the heat transfer surfaces of heat exchangers employing metallic projections, solid fins, or the like, in which the rate of heat transfer between the two fluids is in large part dependent upon the conductivity of the metal.

An improved form of heater having a heat exchanger which has such primary heat transfer surfaces is shown in Figs. 2, 3 and 4, and may be incorporated in the systems shown in Figs. 5, 6 and 7, inclusive, to be described hereinafter.

Referring to Figs. 2, 3 and 4;, the heater comprises an external casing M6, the ends of which are suitably flanged, for attachment to the connecting ducts. A combustion chamber stamping M2 providing a combustion chamber M4, is secured in a flanged inlet head plate Hi6, as by welding. The inlet head plate 1 15 and a similar outlethead plate M8 are secured to a heat exchanger shell I50, preferably by having their flanges welded to the shell. A plurality of tubes 152 are secured in the plates 1% and 148, preferably by having beads E53 formed adjacent their ends, and having their extremities expanded and flanged to form sealed connections with the head plates.

It will be noted that the shell I59 and tubes 152, as well as the heads M6 and 14%, provide primary heat transfer surfaces in that one side of each of these elements is exposed to the heated products of combustion, while the other side thereof is exposed to the ventilating air. The shell 15!] and tubes 52 are preferably made of thin stainless steel sheets and tubes, respectively, with a wall thickness in the order of 0.010 inch.

Thus, while stainless steel is not a very good conductor of heat, the walls of these elements are so thin that heat will be conducted there-' through substantially as fast as it can be transferred to the inner surfaces of the walls and transferred from th'e outer surfaces of the walls. In other words, the rate at which heat will be transferred from the gases of combustion to the ventilating air will depend almost wholly upon stant, and the rate of heat transfer will correspondingly increase, but such increase in the heat transfer will not be reflected in any increase in the temperature of the ventilating air leaving the heat exchanger. This is a very important consideration in many types of installation of aircraft heater-s, When it is desirable that the temperature of the ventilating air supplied to the cabin or other space he maintained below a predetermined value in order to prevent scorching or other damage due to heat, and also is of importance in preventing deterioration or damage to the heat exchanger as a result of the presence of excessively high temperatures.

The fuel supply and combustion apparatus for a heater incorporating a primary heat exchange structure such as shown in Fig. 2, may be of any suitable construction, but is preferably of the general type disclosed in Figs. 2, 3 and 4, and comprises an igniter Well 15 which may be welded to the end of the combustion chamber stamping i 42, and which, as shown in Fig. 3, communicates with the combustion chamber I44 through an opening 56. The air for combustio is supplied through a tube H56, which may, as shown in Fig. 2, project into th casing M0 and have its open end directed opposite to the direction of flow of the air through the casing Mil, or may have its air supplied through a separate scoop 0r ram.

The tube It!) is suitably connected to a Venturi tube carbureting structure I62, which may consist of a die casting I64 including a jet tube 166 for conveying gasoline or other liquid fuel from a float bowl I63 to suitable jet openings I69 at the throat of the Venturi passageway. In lieu of the float bowl M8, the liquid fuel may be supplied to the jet tube I66 from a suitable source, such as an engine fuel pump, with the rate of flow controlled by apparatus responsive both to the atmospheric pressure and to the speed of the air plane, as more fully disclosed in United States M Letters Patent Nos. 2,416,935, dated March l, 1947, and 2,381,358, dated August '7, 1945.

An inlet tube Hi3 projects through the casing ME] and through the side Wall of the combustion chamber stamping I42 into the combustion chamber 144, being bent into substantially semicircular shape as shown in Fig. 3.

The shell 511 is preferably suitably spaced from the casing I40 and held in position therein by a plurality of clips I 76, which may be welded to the shell I5G and detachably secured to the casing Mil by screws I18. An outlet fitting I is preferably provided with a flange welded to the shell 15%? and is adapted to receive an exhaust conduit 181 through which the products of combustion are discharged. This exhaust conduit may be secured to the fitting 18!! by a tight press fit or in any other suitable manner.

In order to assure complete combustion, and to minimize acoustic vibration, and for other reasons, it is frequently desirable to provide open-- ings, such as openings 182, in the head MB of the inlet end of the heat exchanger.

The heater shown in Figs; 2, 3 and 4 is of particular utility whenemployed in a heating systemin which both the ventilating air and the air for combustion are suppliedi from a oommon.

source at thesameor substantiallythe? same:

pressures. Heating: systems of this type are: diazgrammatically shown in Figs. Giand'l; inclusive. In the heating system shown. inli'igs. 5: audit,

the inlet end of the casing ldil'is connected to a. double elbow fittin 2102 which terminates: in a;

scoop 2H2 extending beyond the. skin. 2.14". of' the airplane in which the heater is installed; The

exhaust conduit I3! from the heater'lea'dstoi a jacket 2'! B'which substantiall surrounds the ram portion 212 of. the fitting 210. Thejacket' 216: is

of suitably stream-lined: conformation and has.

an exhaust port 2I8 at. itstrailing end.

While it isusually desirable thatith'ezheatoutput of the heater increasezas thespeed of the.

the velocity of. flow of theair for combustion and' the ventilating air.

The position of the valve'2'20 is preferably made.

responsive to the difference between the pressure in the inlet fitting 2 0. and atmospheric pressure, and means for accomplishing this result is diagrammatically illustrated as comprising motor device 222, the m'ovable'element of which is connectcd'by. an actuating rod 224: with the valve 229;. The motor 222" is responsive to'the pressure in the inlet fitting. by. virtue of an opening 226- inthe fitting Zilland by virtue of a connection with the atmosphere througha-zconduit'228i The valve 229],- togetheriwithits motor device 222, may be arranged'to cause the heaterto have substantially-uniform heat output at all speeds,-

or to have. the heat output increase somewhat' with increased speed, dependingupon the rates of heat loss from the space being heated at various airplane speeds.

Because of the fact that the products of combustion from the heater flow from the exhaust conduit l8! through the space between the scoop 2i2 and the jacket Elli, and since the exhaust gases are usually atxa fairly'high temperature, the scoop 2l2 willibe retained at a sufiiciently high temperature to prevent the formation of ice,

or to remove any ice which has collected thereon prior to-the. time the. heater started operation. The jacketing of the inlet air scoop also has the advantage of preheating the air. intake slightly,

with the consequence that thevaporizationof the fuel is somewhat improved;

It will be understood that the heater within the casing lil'may bev of: any suitable type, but that the best results are obtained: when' the heater includesa heat exchanger havingprimary heat transfer surfaces, such as the heater shown in Figs. 2, 3 and-4.

In the form of theinvention shown in Fig. 7,

a heater such as shown in Figs..2, 3 and 4, and including a casing Milihas'an inlet duct 280'conduit NH. and circulate about the inlet duct 280 due to the provision ofa jacket 288- surrounding the major portion-of'this:duct', the products of combustion being exhaustedthrougha trailing discharge pipe- 290'.

The inlet duct 280' has a Y'-b-ranch 284" The ventilating air is v an elbow duct 294.

In the forms of'the heating: systems: disclosed herein. in which; scoops are used, they are illus- 5 tratedi asbeingof: the fixed type; It. will'be understood; however; that the constructions'may be suitably modified. to enable the scoops to be retractible'to. positions: in which they are flush or substantially flush with the skinof: the airplane. 0. Thus, when the heating system is not in use,

the. scoop or scoops may be retracted to reduce the frontal area. of the airplane;. and thereby reduce the drag.

While I. have shown: and described particular embodiments ofmy invention, it will be apparent to those. skilled in the art; that the underlying principles'of the invention maybe. embodied: in numerous. other forms without. departing from the. underlying principles of: the. invention. I therefore desire, by the following claims, to. include'withinthe scope of my invention,.all such modifications and variations .of the. invention disclosed by which substantially the: results of the invention may be obtained-by the useofsubstantially. the same or equivalent means.

I claim:

1. In an aircraft heating-system having aco'mbustio chamber. and a'heat exchanger. connected to receive products of combustion: therefrom, means'including an opening: to. the atmosphere directed forwardly. of. the airplane to supply'combusti'on. air tosaid chamber. and to supply ventilatin'g. air to. said heat exchanger; a. jacket around aportiorrof said means, ventilating air duct means connected to. the outlet of: saidheat 'exchanger for conveying heated air therefrom to a space tobe heated; andconduitimea'ns including said jacket for. conveying the; products of combustion fromsaidheat exchanger. to the atmosphere.

2..In. an. airplane heating system, the combination of: a combustionv chamber; a heat exchanger, airv ram meansfor. supplying air for combustion to said combustion chamber and for supplying ventilating air to said heat exchanger, said-air: ram means supplying air at thedynamic pressure resultant from the flight of the airplane. through the atmosphere, avalve forregue lating the rate of flow of air through said air ram: means, and means responsive to the pressure. of the air in said air ram to move. said valve towardclosed. position upon an increase in pressure and toward open position-upona decrease in pressure.

3. An anti-icing air-scoop, comprising a structure'projecting from" the wall of an aircraft, said structure providing an air inlet passage having an opening adapted to faceforwardly upon an.

aircraft and a space for exhaust gases com- 1 pletely surrounding said air inlet passage at said opening and open at the rear. to the atmosphere, said structure being adapted to project into an air stream created by operation of said aircraft.

4. An. aircraft heater installation, comprising an aircraft, a heater on said aircraft and having a combustion chamber andaheat exchanger for receiving hot products. of combustionv fromsaid.

chamber, means providing a passage including an opening to atmosphere directed toward the front of the aircraft to supply air to said combustion chamber, an exhaust jacket closed at its forward portion surrounding a portion of said passage and extending to a point immediately adjacent said opening, said jacket beingv open to the-at- 7 'mosphere at its rear portion, and a' pipe for conducting exhaust gases from said heat exchanger to said jacket.

5. An aircraft heater installation of the class described comprising an aircraft, a heater on said aircraft and having a combustion chamber and a heat exchanger for receiving hot products of combustion from said chamber, an anti-icing scoop having means providing a passage including an opening to atmosphere directed toward the front of the aircraft to supply air to said chamber, means forming an exhaust jacket surrounding a portion of said passage and having a part immediately adjacent said opening, said jacket being open to the atmosphere to the rear of said opening, and means for conducting exhaust gases from said heat exchanger to the forward portion of said jacket.

HENRY J. DE N. MoCOLLUM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,321,940 Robertson June 15, 1943 1,357,598 Thompson Nov. 2, 1920 2,286,853 Holthouse June 16, 1942' 2,262,003 Huffman Nov. 11, 1941 2,179,500 Diehl Nov. 14, 1939 2,230,446 Baker Feb. 4, 1941 2,265,168 Huffman Dec. 9, 1941 2,330,298 McCollum Sept. 28, 1943 2,364,458 McCollum Dec. 5, 1944 

